1. Field of the Invention
The present invention relates to paper-making machines, and, more particularly, to paper-making machines having a wet end with a liquid collection device.
2. Description of the Related Art
A paper-making machine includes a forming fabric, traditionally known as a "wire", in a forming section at the wet end of the machine. The fiber suspension is discharged from a headbox onto the forming fabric. More than one forming fabric may be provided in the forming section of the paper-making machine for sequentially contacting and/or carrying the wet fiber web through the wet end of the machine. Each forming fabric typically is in the form of a woven polymeric mesh material with voids defined by the mesh. A portion of the water in the fiber suspension passes through the voids in the forming fabric, while another portion of the water in the fiber suspension may be retained within the voids as a result of adhesion forces between the water and forming fabric.
Each forming fabric is typically in the form of an endless fabric carried by a plurality of rolls. As the forming fabric approaches a roll at running speed, a converging area is defined by the forming fabric and roll. Since the forming fabric and roll are of course not perfectly smooth surfaces, some frictional resistance between the forming fabric, roll and air in the converging area is created which causes a flow of air toward the point of contact between the forming fabric and roll. The flowing air is pushed out through the forming fabric at the contact location between the forming fabric and roll, thus creating a mist of water on the side of the forming fabric opposite the roll. As the forming fabric is carried around a portion of the periphery of the roll, some of the water in the voids of the forming fabric is attracted via adhesion forces to the surface of the roll. At the point of separation or divergence between the forming fabric and roll, the adhesion forces between the water and roll cause at least a portion of the water in the forming fabric to be drawn out of the voids in the forming fabric and fall via gravitational force from the diverging area between the forming fabric and roll.
A doctor element, such as a doctor blade, can be placed such is that it bears against a roll and cleans the roll by scraping fibers off the roll. A water shower is typically provided in association with the doctor blade for lubricating the doctor blade as it bears against the roll. The shower directs a stream of water against the roll across the width of the doctor blade and on the approach side of the doctor blade. The water inhibits wear and heating as a result of the frictional forces between the doctor blade and roll.
A liquid collection device including a suction chamber and an air/water separator can be used to catch water precipitating from the forming fabric and the from the roll in the area between the forming fabric and the doctor element. The suction chamber, extending across the width of the forming fabric, includes an at least partially open top and an outlet. The open top of the suction chamber can be placed between and below the area of divergence between the forming fabric and roll and the doctor element in order to catch the precipitating water. The air/water separator receives liquid from the suction chamber outlet.
It is known to mount a vacuum generating device on top of an air/water separator in order to generate a vacuum within the suction chamber to draw the liquid within the suction chamber into the air/water separator. Such a vacuum generating device can be in the form of a centrifugal blower or fan having a metal hub and vanes and which is mounted on top of the air/water separator. The centrifugal blower draws the water as well as a mixture of fiber laden mist and air through the suction chamber, into the air/water separator, and blows the fiber/mist/air mixture into the ambient environment.
A problem with a blower or fan as described above is that the moisture in the air drawn by the blower allows the fibers to adhere to the vanes or blades of the blower. These fibers can build up on the vanes to the point where the weight of the fibers causes the blower to be out of balance. Due to the added load of this imbalance, the blower ball bearings may fail as a result thereof. The problem is exacerbated by the relative weightiness of the metal material of which the blower vanes and hub are formed. Because of the weight of the blower vanes and hub, more stress is placed on the ball bearings and any rotational imbalance is magnified.
Another problem is that the vanes and hub are formed of a relatively heavy material, such as metal, and may be out of balance. The high rotational speed of a blower in a paper machine combined with the relative weightiness of the vanes and hub may cause higher amplitude vibration of the blower in operation. This higher amplitude vibration may lead to premature bearing failure.
It is also known, with such a blower configuration, to periodically disassemble the centrifugal blower and wash the vanes to rid them of the accumulated fibers. This, however, is an expensive process which may require frequent downtime.
What is needed in the art is a centrifugal blower for use in the wet end of a paper-making machine which is lighter, stronger, repels fiber laden water, and may be cleaned "on the fly," thus being able to rotate faster, being less susceptible to rotational imbalance and reducing downtime associated with cleaning.